Pet Peeves
The center of mass of the human body is actually slightly below the navel. In fact, this is actually a good target, particularly if your shot is off center. The best place for a shot to the pelvis is between the sacrum (the fused portion of the spine that forms the central part of the rear of the pelvis) and the hip joint. This area is known as the weight-bearing triangle and is more likely to be broken by handgun bullets than the heavier sacrum. Further, this area also contains a
large bundle of blood vessels and nerves.
Head shots are extremely difficult to make on moving people who realize that you're trying to shoot them in the head. Further, only a relatively small portion of the head contains the "off switch" or brainstem. Additionally, the relatively thick portion of the skull that protects most of the brain is not that easy to penetrate with handgun bullets, particularly if a rounded surface of the bullet's noses contacts the rounded surface of the skull.
While most of us are limited to shooting two-dimensional paper targets, not too many people bother to try to visualize them in three dimensions, to envision where the vital organs would be if the shot penetrates from anything other than a straight-on, level angle.
For anyone interested in more detailed rants on this topic, including a useful image of the anatomy of the pelvis, I have brief articles on Aiming Points, Head Shots and Pelvis Shots posted on the
Naked Emperor page of my website.